For conventional laminates for printed circuits, brominated flame retardants, especially tetrabromobisphenol-A epoxy resin, are usually used to achieve flame retardancy. Such brominated epoxy resin has better flame retardancy, but will produce hydrogen bromide during combustion. In addition, carcinogens, such as dioxin, dibenzofuran and the like, have been detected recently in the combustion products of electrical and electronic equipment wastes containing halogens, such as bromide, fluorine and the like. Thus the application of brominated epoxy resin has been limited. Two European Union environment-protecting directives, Waste Electrical and Electronic Equipment Directiveand The Restriction of the use of Certain Hazardous Substances in Electrical and Electronic Equipment, were formally implemented on Jul. 1, 2006. The development of halogen-free flame-retardant copper-clad laminates became a hot spot in the industry, and the cooper-clad laminate manufacturers have launched their own halogen-free flame-retardant copper-clad laminates in response.
Meanwhile, with the high speed and multifunctional development of information processing of consumer electronic product, the application frequencies continue to increase. Besides increasing environmental requirements, there are increasing requirements on low dielectric constant and dielectric dissipation values. Thus it becomes a pursuit not to decrease Dk/Df in the substrate industry. For conventional FR-4 materials, dicyandiamide is mostly used as a curing agent. Such a curing agent has a tertiary reactive amine and has better processability. However, the cured product has a lower thermal decomposition temperature due to its weaker C—N bond which is easy to split under high temperature, so that it cannot meet the requirements on thermal resistance for lead-free processes. In this context, they began to use phenolic resin as the epoxy curing agent in the industry with the large scale implementation of lead-free process in 2006. Phenolic resin has a benzene ring structure of high density, so that the epoxy-cured system has excellent thermal resistance. However, the dielectric properties of the cured products have a tendency to deteriorate.